This application claims the Paris Convention priority right of Japanese Patent Application No. Hei 10-371573 filed on Dec. 25, 1998, the entire disclosure of which is incorporated by reference.
(i) Field of the Invention
The present invention relates to a multi-point thin portion compression molding method and a multi-point thin portion compression mold for use in this method, particularly to a multi-point thin portion compression molding method of filling a metal mold with molten resin and pressurizing and compressing a molded material by a movable telescopic member in a cavity to form a plurality of thin portions and a multi-point thin portion compression mold for use in this method.
(ii) Description of the Related Art
In a conventional art, a case formed by an injection molding technique is frequently used in the exterior member of an electronic apparatus. For this electronic apparatus case, in recent years, there has been a demand for reduction in size for carrying and other use purposes. Moreover, for the electronic apparatus case, there are demands for the integration of a circuit substrate and the thinning of the case in order that the increasing number of electronic components with various additional functions are efficiently contained inside. Particularly, for example, in mobile communication terminals such as a PHS phone and a cellular phone, the reduction in size for carrying and the thinning of the case for efficiently containing the increasing number of internal components with various additional functions are most important. FIG. 11 is a sectional view showing a conventional injection mold for forming such case. Moreover, FIG. 12 is a perspective view of a case 70 of a cellular phone formed by the injection mold shown in FIG. 11. Furthermore, FIG. 13 is a sectional view of a section taken along line Ixe2x80x94I shown in FIG. 12.
As shown in FIG. 11, the conventional injection mold is constituted of a pair of a fixed metal mold 60 and a movable metal mold 50 which are opened/closed, and attached to a predetermined mold opening/closing apparatus (not shown) and driven. Here, the movable metal mold 50 is movable in an arrow direction shown in FIG. 11, and attached to or detached from the fixed metal mold 60. Moreover, a cavity space 61 having a molded material shape is formed between the fixed metal mold 60 and the movable metal mold 50 when the mold is closed. This cavity space 61 is connected to a gate 62 via which molten resin 1 is supplied from the outside of the fixed metal mold 60, and this gate 62 is provided with a spool 62a and a runner 62b which are formed in the fixed metal mold 60 and the movable metal mold 50, respectively. In the injection mold shown in FIG. 11, the gate 62 is formed in a submarine gate (tunnel gate) shape.
To form the molded material by the conventional injection mold formed as described above, the movable metal mold 50 is placed in contact with the fixed metal mold 60 to close the mold, the movable metal mold 50 is pressed onto the fixed metal mold 60 to clamp the mold, then the cavity space 61 is filled with the molten resin 1, and the molten resin 1 is cooled to form the molded material. Subsequently, the movable metal mold 50 is detached from the fixed metal mold 60 to open the mold, and an ejector pin (not shown) is allowed to protrude from the movable metal mold 50 so that the molded material can be taken out.
The cellular phone case 70 formed by the above-described conventional injection mold will next be described in detail with reference to FIG. 12. As shown in FIG. 12, the cellular phone case 70 formed by the conventional injection mold is provided with a circuit substrate 80 with a plurality of electronic components 82 mounted thereon to form a high frequency circuit section. In this case, when the circuit substrate 80 is attached inside the case 70, the high frequency circuit section is requested to be shielded. Therefore, in the case 70, a shield wall 76 for closing and shielding the high frequency circuit section is formed.
Here, the circuit substrate 80 with the electronic components 82 higher than the shield wall 76 mounted thereon is attached to the case 70, and recessed thin portions 72 are formed so that the high electronic components 82 can be contained inside the shield wall 76. The recessed thin portions 72 can be formed by disposing protrusions in the cavity space 61 of the movable metal mold 50 shown in FIG. 11. Since the case 70 is provided with the thin portions 72 in this manner, an interval J between the surface of the circuit substrate 80 and the outer surface of the case 70 shown in FIG. 13 can be formed to be thin, thereby thinning the entire cellular phone case.
However, in the conventional injection molding method, there are design restrictions determined by the resin property and metal mold. For example, with a large thickness, hardening requires much time and disadvantages such as sink marks are generated. On the other hand, with a small thickness the molten resin fails to flow in the terminal end of the injection molded material. The thickness of the generally used injection molded material is in a range of about 0.8 mm to 1.5 mm at standard. Moreover, in the design of the injection molded material, considerations are required so that the thickness of the injection molded material is as uniform as possible. Particularly, in the injection molding, when the cavity space is filled with the molten resin, the surface of the resin flowing along the wall surface of the cavity space is quickly cooled and hardened, and so-called skin layers 1a are formed as shown in FIG. 13. The flow of the molten resin is further deteriorated by the skin layers 1a in the thin portions 72 shown in FIG. 13.
Therefore, in the case 70 shown in FIG. 12, since the thickness of the thin portion 72 is not uniform, the flow of the molten resin supplied via the gate 62 is deteriorated. This causes the insufficient filling of the case 70, and welds 70a by the resin flow in the thin portions 72 shown in FIG. 12. Moreover, in the usual injection molding, since the injection molded material is cooled as it is without being pressurized during the cooling process, the sink marks are generated on the surface of the molded material because of a difference of shrinkage factor between the thin portion compressed during the cooling process and the usual thick portion.
There is a compression molding method as a method for solving the above-described disadvantages. This compression molding method, in which the resin in the cavity is pressurized during the cooling process, has been noted in recent years as a technique of filling the inside of the metal mold with the resin and subsequently moving a movable telescopic member to compress the resin so that the sink marks are locally controlled or the opening and thin portions can be formed without any welds. Such prior art is disclosed, for example, in Japanese Patent Application Laid-Open No. 230534/1998. FIG. 14 is a sectional view showing such conventional compression mold. Moreover, FIG. 15 is an operation explanatory view showing an operation of forming the molded material by the compression mold shown in FIG. 14, FIG. 15A shows the filled state with the molten resin, FIG. 15B shows that the molten resin is compressed by the movable telescopic member, and FIG. 15C shows that the inside of the cavity is filled by the movable telescopic member. Moreover, FIG. 16 is a perspective view showing an IC card formed by the compression mold shown in FIG. 14.
As shown in FIG. 14, the conventional compression mold is constituted of a pair of a fixed metal mold 100 and a movable metal mold 90 which are opened/closed, and attached to a predetermined mold opening/closing apparatus (not shown) and driven. Here, the movable metal mold 90 is movable in an arrow direction shown in FIG. 14, disposed to be attached to or detached from the fixed metal mold 100, and further provided with a movable telescopic member 92 passed through the inside and movable in the arrow direction shown in FIG. 14. Since there is a high possibility that the molten resin 1 enters between the movable telescopic member 92 and the movable metal mold 90 during the compression by the movable telescopic member 92, burrs are generated on the molded material. Therefore, engagement is most important in the interval between the movable telescopic member 92 and the movable metal mold 90. The engagement between the movable telescopic member 92 and the movable metal mold 90 is usually preferably set in a range of 5xcexc to 4xcexc. Moreover, a cavity space 99 having a molded material shape is formed inside between the fixed metal mold 100 and the movable metal mold 90 when the mold is closed. The cavity space 99 is provided with a gate 102 via which the molten resin 1 is supplied from the outside of the fixed metal mold 100.
When the molded material is formed by the conventional compression mold formed as described above, the movable metal mold 90 is placed in contact with the fixed metal mold 100 to close the mold, and the mold is clamped by pressing the movable metal mold 90 onto the fixed metal mold 100. Subsequently, as shown in FIG. 15A, the cavity space 99 is filled with the molten resin 1. In this case, as shown in FIG. 15B, the compression of the movable telescopic member 92 is started in the arrow direction shown in FIG. 15B while the cavity space 99 is sufficiently filled with the molten resin 1. Thereby, the molten resin 1 is supplied toward an unfilled portion 99a shown in FIG. 15B by the compression pressure of the movable telescopic member 92, and the inside of the cavity space 99 is entirely filled by the compression of the movable telescopic member 92 to a predetermined position as shown in FIG. 15C. As described above, since the conventional compression molding method comprises moving either the whole or a part of the metal mold by a compression molding apparatus mechanism or a separate mechanism and pressurizing the resin in the cavity, the defective phenomena such as the sink marks and welds of the molded material because of the volume decrease of the molten resin are eliminated.
As the molded material formed by the above-described conventional compression mold, for example, there is a main body 112 of an IC card 110 shown in FIG. 16. The main body 112 of the IC card 110 is formed in a thin rectangular flat plate shape, a flat surface is formed on one surface, and a recess portion 112a is formed on the other surface by compression by the movable telescopic member 92 in the above-described cavity of the compression mold. Moreover, the main body 112 is about 1.2 mm thick in the flat rectangular shape, and the ultra thin portion compressed by the movable telescopic member 92 on the bottom surface of the recess portion 112a is about 0.16 mm. Then, the IC card 110 is formed by housing an IC module 114 in the recess portion 112a of the main body 112. Therefore, since this main body 112 is formed by the conventional compression mold, the recess portion 112a can steadily be formed without any defective phenomena such as sink marks and welds.
However, in the conventional compression mold, it is difficult to dispose a plurality of recess portions 112a shown in FIG. 16, and the molding conditions such as a compression stroke, injection pressure, injection speed, metal mold temperature and pressure adjustment inside the metal mold are complicated in the application to the molded material provided with a complicated shape, for example, like the cellular phone case shown in FIG. 12. Moreover, for the cellular phone case, by the demand for the thinning of the case as described above, the molded material is formed in the thin portion having a thickness of 0.4 to 0.6 mm, and further the ultra thin portion having a thickness of 0.1 to 0.25 mm has to be formed by the compression by the compression mold.
As described above, in the conventional injection molding and compression molding methods, there is a disadvantage that it is difficult to provide the thin portion with a thickness of 0.4 to 0.6 mm and to further form a plurality of ultra thin portions with a thickness of 0.1 to 0.25 mm compressed by the compression molding on the case.
Moreover, since it is difficult to form a plurality of ultra thin portions by further compressing the thin portions, it is difficult to manufacture the portable case of the electronic apparatus reduced in weight and thickness. Additionally, when a plurality of ultra thin portions are formed by the conventional metal mold, the metal mold manufacture cost is disadvantageously increased.
The present invention has been developed to solve the above-described problems, and an object thereof is to provide a multi-point thin portion compression molding method and a multi-point thin portion compression mold for use in this method in which a plurality of ultra thin portions can steadily be formed by compression molding.
To achieve the above-described object, according to the present invention, there is provided a multi-point thin portion compression molding method which comprises disposing a pair of metal mold apparatuses opened/closed to each other to form a cavity having a molded material shape therebetween when a mold is closed, disposing at least one movable telescopic member on one opened/closed movable metal mold of the metal mold apparatuses for protruding toward the other fixed metal mold in the cavity by a metal mold mechanism or a separate mechanism, forming a recess portion for a rib on the movable metal mold for surrounding the periphery or a part of this movable telescopic member, closing the movable metal mold and the fixed metal mold, filling the cavity other than the recess portion with molten resin, subsequently allowing the movable telescopic member of the movable metal mold to protrude, compressing the molten resin in the cavity, allowing the molten resin to escape to the recess portion, and adjusting pressure applied to the inside of the metal mold so that at least one ultra thin portion is formed on a molded material by stable compression.
Here, the thickness of the molded material is formed to be a thin thickness in a range of 0.4 to 0.6 mm, and the thickness of the ultra thin portion of the molded material is formed to be a film-like ultra thin thickness in a range of 0.1 to 0.25 mm by compression of the movable telescopic member. Moreover, the movable metal mold and the movable telescopic member are preferably breathed by disposing a vent portion having a gap of 15xcexc to 20xcexc on both or either one of the center and the periphery of the movable telescopic member. Furthermore, the recess portion is preferably provided with a burr preventive portion to prevent burrs from being generated by the gap of the vent portion. Additionally, it is preferable to employ the molded material in cases of electronic apparatuses reduced in size such as a PHS phone and a cellular phone.
According to another aspect of the present invention, there is provided a multi-point thin portion compression mold for use in the multi-point thin portion compression molding method, which comprises a pair of metal mold apparatuses opened/closed to each other to form a cavity having a molded material shape therebetween when a mold is closed, at least one movable telescopic member disposed on one opened/closed movable metal mold of the metal mold apparatuses for protruding toward the other fixed metal mold inside the cavity by a metal mold mechanism or a separate mechanism, and a recess portion for a rib formed on the movable metal mold for surrounding the periphery or a part of the movable telescopic member.
Here, the thickness of the molded material is formed to be a thin thickness in a range of 0.4 to 0.6 mm, and the thickness of an ultra thin portion of the molded material is preferably compressed and formed to be a film-like ultra thin thickness in a range of 0.1 to 0.25 mm by moving the movable telescopic member. Moreover, the movable metal mold and the movable telescopic member are preferably provided with a vent portion having a gap of 15 xcexc to 2xcexc for discharging gas to both or either one of the center and the periphery of the movable telescopic member. Furthermore, the recess portion is preferably provided with a burr preventive portion to prevent burrs from being generated by the gap of the vent portion. Additionally, it is preferable to employ the molded material in the cases of the electronic apparatuses reduced in size such as the PHS phone and the cellular phone.